The present invention relates to an antenna arrangement comprising a substantially planar patch conductor, and to a radio communications apparatus incorporating such an arrangement.
Wireless terminals, such as mobile phone handsets, typically incorporate either an external antenna, such as a normal mode helix or meander line antenna, or an internal antenna, such as a Planar Inverted-F Antenna (PIFA) or similar.
Such antennas are small (relative to a wavelength) and therefore, owing to the fundamental limits of small antennas, narrowband. However, cellular radio communication systems typically have a fractional bandwidth of 10% or more. To achieve such a bandwidth from a PIFA for example requires a considerable volume, there being a direct relationship between the bandwidth of a patch antenna and its volume, but such a volume is not readily available with the current trends towards small handsets. Further, PIFAs become reactive at resonance as the patch height is increased, which is necessary to improve bandwidth.
A PIFA intended for use in a dual-band application typically comprises two resonators with a common feed point. An example of such an antenna is disclosed in European patent application EP 0,997,974, in which two PIFA antennas are fed from a common point and share a common shorting pin. However, use of multiple resonators further increases the antenna volume.
An object of the present invention is to provide a planar antenna arrangement requiring a substantially smaller volume than known PIFAs while providing similar dual-band or multi-band performance.
According to a first aspect of the present invention there is provided an antenna arrangement comprising a substantially planar patch conductor supported substantially parallel to a ground plane and a feed conductor connected to the patch conductor, wherein the patch conductor is electrically insulated from the ground plane at operational frequencies of the antenna arrangement and wherein the feed conductor is coupled to a matching network arranged to provide a match to the antenna at a plurality of discrete frequencies.
Such an antenna arrangement differs from a conventional PIFA in that there is no grounding conductor connected between the patch conductor and the ground plane. By eliminating this grounding conductor and performing dual-band (or multi-band) matching with external circuitry, a better match can be achieved over a wide range of frequencies, enabling similar performance to conventional PIFA antennas to be achieved from a reduced volume and with a less complex antenna.
According to a second aspect of the present invention there is provided a radio communications apparatus including an antenna arrangement made in accordance with the present invention.
The present invention is based upon the recognition, not present in the prior art, that by eliminating the grounding pin from a PIFA and making use of a separate multi-band matching network, a significantly reduced antenna volume is possible.